The present invention relates generally to teaching devices, and more particularly to laboratory apparatus for teaching the concepts of electrochemical principles.
The production of an electric current through the utilization of an oxidation-reduction reaction is a well-known concept in electrochemistry. It is also a concept that is taught in many, if not all, high school and college chemistry courses, and typically forms the basis of electrochemistry experiments performed by students in laboratory sections of the class.
Generally, this concept is taught in the school laboratory by providing the student with the materials to construct two or more dissimilar electrodes so that the potential difference of each electrode couple can be measured. Usually, the materials the student receives include at least a pair of metallic salt (reactant) solutions such as, for example, a ZnSO.sub.4 solution and a CuSO.sub.4 solution, and apparatus that holds the solutions in a manner that keeps them from mechanically mixing with one another, yet permits the passage of ions from one to the other. A zinc metal electrode and a copper metal electrode are respectively placed in the ZnSO.sub.4 and CuSO.sub.4 solutions to create what is known as an electrochemical or galvanic cell. The student then determines the voltage potential by measuring the electron flow from the zinc electrode to the copper electrode with a commonly available voltmeter.
One method of mechanically isolating, yet providing ion travel between, the reactant solutions is to provide some type of a porous partition that separates the solutions, thereby creating the galvanic cell. This method requires a container that is divided into two liquid-receiving chambers by a porous material--usually a porous porcelain cup that holds one of the reactant solutions and rests in the other reactant. Alternately, the solutions can be placed in separate beakers. A "salt bridge," usually a U-shaped glass tube containing a solution of an electrolyte (such as NH.sub.4 NO.sub.3 or KNO.sub.3) and stoppered at each end with glass wool, forms the connection between the two solutions for the passage of ions. The salt bridge can also be constructed by filling the tube with a gelatinous material in which is dissolved a salt (such as 3.0 g of agar-agar added to 600 ml of boiling 1 M potassium nitrate solution), forming the requisite electrolyte bridge.
Unfortunately, there is considerable expense involved in obtaining the necessary above-described apparatus and materials. A substantial amount of glassware is called for, particularly in chemistry laboratories of schools of any size. This, in turn, can create inventory problems: Where and how is the apparatus to be stored? Cleaning the apparatus, both before and after use, presents not insubstantial problems and expense due to breakage. Since much of the apparatus used (glass beakers, glass tubes and porous porcelain cups) is relatively fragile, allowing students to clean the materials can increase the expense of laboratory equipment by the breakage that will typically be encountered. If hired help is to clean the apparatus the cost goes up accordingly, depending not only on how much must be paid the help but, to a certain extent, on the manual dexterity of the help. And, even if lab personnel rather than students clean the apparatus after use, breakage still remains a problem by students since they typically perform their own set-up of experiments.
Further, because it is desirable that whatever is used for such electrochemical (teaching) experiments be usable in other learning experiments in the lab, relatively large beakers (i.e., on the order of 450 ml) are used. This causes consumption of larger amounts of reactants than really necessary, increasing the expense to the school. In addition, disposal of the solutions (both the reactants and the bridge electrolyte) can create difficulty if pollution problems are to be avoided--particularly for larger schools having a high proportion of chemistry students.
In addition, it can be tedious and time-consuming to clean the glassware, particularly U-shaped tubes, to avoid contamination. And, when using a gelatinous substance (i.e., agar-agar) as the bridge electrolyte, pains must be taken to avoid bacterial contamination of the substance. A salt bridge, after one use, cannot be used again until it is meticulously cleaned and repacked.
Finally, the time required for assembly and disassembly of galvanic cells in a school laboratory using present techniques and apparatus seriously reduces the number of electrochemical set-ups and experiments that can be made by a student. If more time is allotted to teach, in the laboratory, some of the finer aspects of electrochemistry and oxidation-reduction reactions--such as entropy, thermodynamics and the way galvanic cells of different chemical make-up react--other portions of the chemistry course may suffer accordingly.